The present invention relates to a device for coupling between a single-ended circuit and a balanced circuit, and particularly to such a device which is impedance matched.
A large number of devices are available for converting between single-ended and push-pull signal circuits at high frequencies and are often referred to as baluns. These devices can perform impedance transformation and generally behave as high-frequency transformers having a single-ended side and a push-pull side. The various designs differ in regard to the frequency band for which they are intended, the power handling capacity, and the circuit impedances. The impedance transformation can be accomplished by transformer turns ratio, and by various configurations of series and parallel transmission lines. Many of these devices are awkward in size and may not provide an accurate impedance transformation. For instance, if the impedance transformation is a function of a turns ratio between coils, only a ratio between integral numbers of turns is ordinarily available and is not easily changed from one application to another.